1. Technical Field
The present disclosure relates to an overvoltage protection device, and more specifically to an overvoltage protection device capable of protecting a power supply line.
2. Description of the Related Art
An overvoltage protection device is a component or circuit which turns on when the voltage thereacross exceeds a given threshold, called breakdown voltage, and generally designated as VBR.
A first type of protection component is of avalanche diode type, with a current-vs.-voltage characteristic illustrated in FIG. 1. When the voltage across this component exceeds breakdown voltage VBR, the component turns on. Ideally, the voltage across the component remains equal to VBR while the current increases. Indeed, as shown in FIG. 1, the characteristic is not vertical and the voltage across the component exceeds value VBR while the overvoltage is absorbed, that is, a current I of strong value crosses the component.
A disadvantage of this type of component is that during the overvoltage absorption phase, the voltage across the component remains greater than or equal to breakdown voltage VBR, that is, during this phase, the component has to absorb a power greater than VBR×I. This results in having to form a component having sufficiently large size to be able to absorb this power without being destroyed. Currently, for voltages VBR greater than 100 volts, for example, on the order of 300 volts, this results in component sizes greater than several cm2, for example, on the order of 10 cm2. Such components are however made in the form of a stack of diode chips, for example, a stack of fourteen elementary components each having a surface area of 8.6×8.6 mm2 to reach a 430-V breakdown voltage. Such components are thus expensive and bulky.
A second type of protection component is of break-over type, of Shockley diode type, or of gateless thyristor type. The current-vs.-voltage characteristic of a break-over component is illustrated in FIG. 2. When the voltage across the component exceeds breakdown voltage VBR, this voltage rapidly drops and then follows a substantially vertical characteristic I.
An advantage of this second type of component is that the power dissipated by the overvoltage in the component is low as compared with the power dissipated in a device of avalanche diode type, given that the voltage across the component is very low during the overintensity flow. A disadvantage of this second type of component is that, as long as there is a voltage across the component, said component remains on, the protection component only turning back off if the voltage thereacross is such that the current in this component becomes smaller than a hold current Ih. For a protection component having its breakdown voltage VBR approximately ranging from 50 to 1,000 volts, this hold current currently has a value approximately ranging from 100 mA to 1 A according to the breakdown voltage of the component.
Accordingly, break-over type protection components are reserved for circuits where these components are intended to protect a line having an operating voltage crossing zero values—this being in particular true for a data transmission line.
As illustrated in FIG. 3, if a line L1 forming a power supply line connected to the output of a power supply device such as a solar power plant 10, for example connected to an inverter 12, is desired to be protected, a break-over protection component can normally not be used since, after the occurrence of an overvoltage, for example corresponding to a lightning surge on line L1, the voltage on line L1 remains positive and the protection component remains conductive.
As illustrated in FIG. 4A, after application of the overvoltage, voltage VDC at the output of power supply source 10 is short-circuited and a short-circuit current ISC flows therein. The source sees across its terminals internal resistance Ri and on-state resistance RD of the protection diode. A voltage VD=VDC(RD/(Ri+RD)) then exists across the protection diode.
FIG. 4B shows a portion of the characteristic curve of the diode corresponding to this specific case. In most practical configurations, potential VD corresponding to short-circuit current ISC is much greater than voltage Vh corresponding to hold current Ih of the break-over component. As an example, for a 150-mA hold current Ih, voltage Vh may be on the order of 2V. It is thus a priori not possible to use a break-over component to protect a D.C. power supply line. Protection devices of avalanche diode type, which have significant surface areas and thus a high cost, thus are used.
It is here desired to overcome this disadvantage.